<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*字体大小,否则无效*/
        div {
            font-weight: 700;
        }

        h1 {
            font-weight: 400;
        }
    </style>
</head>
<body>
<!--文字默认是16px-->
<div>段落文字</div>
<h1>一级标题</h1>
</body>
</html>